Detector's specifically optimized for X-ray Photon Correlation Spectroscopy (XPCS) involve imaging “speckle” patterns produced when a coherent beam of x-rays scatters off a disordered sample. The speckle pattern is essentially the superposition of many single-particle diffraction patterns produced by the atoms within the sample. As the atoms undergo motion, the speckle pattern changes, so XPCS can be used to study atomic dynamics at very short time and distance scales. Use of XPCS will continue to expand for applications associated with x-ray light sources in coming years, particularly as synchrotrons upgrade to increase coherence.
Speckle patterns produce an anomalously weak signal. With average pixel occupancies >>1% XPCS is not well suited to a traditional x-ray area detectors which read out every pixel on every exposure. Much of the data throughput would be spent processing empty pixels.